1. Technical Field
This invention relates generally to an apparatus and method for controlling heat losses in the combustion chamber of an internal combustion engine, and more particularly to such an apparatus and method for the active control of the combustion rate in an internal combustion engine.
2. Background Art
The operating setpoints of modern reciprocating engines are best described as a compromise between settings that allow highest engine efficiency, settings that reduce regulated emissions and settings that reduce the tendency for the engine to knock. The compromised setpoints define engine performance/emissions tradeoffs that are far from optimal solutions for any one of the individual performance or emissions targets. Therefore, the design of an engine""s combustion chamber is typically directed at satisfying a range of operating conditions most common to the end-user. However, because an engine must often operate for short periods at off-design conditions, compromises in combustion chamber design must be made to ensure that emissions regulations are met, or that engine damage does not occur.
Several approaches have been proposed for static, or steady state, control of heat loss through the walls of a combustion chamber when an engine is operating at off-design conditions to reduce possible damage to the engine and minimize any compromise of emissions. For example, U.S. Pat. No. 4,413,596, granted Nov. 8, 1983, to Tsutoma Hirayama for an ENGINE COOLING SYSTEM WITH OPTIONALLY COMMUNICABLE HEAD COOLING CIRCUIT AND BLOCK COOLING CIRCUIT, AND METHOD OF OPERATING THE SAME, describes the use of separate block and cylinder head cooling systems with active control of each system. In the Hirayama system, engine knock is controlled by cooling the cylinder head. More recently, U.S. Pat. No. 5,934,228, granted Aug. 10, 1999, to Fred Wheat for an ADJUSTABLE COMBUSTION CHAMBER INTERNAL COMBUSTION ENGINE describes a variable compression ratio device and modulates the compression ratio for optimized engine performance. The Wheat patent further describes the use of reciprocating engine sleeves to optimize fuel-air delivery timing in a two-stroke engine.
A combustion chamber design and method for steady state combustion control is described in co-pending U.S. application Ser. No. 09/974,210, filed Oct. 10, 2001, by Charles Edward Roberts, Jr., a co-inventor of the present invention, for a MULTI-ZONE COMBUSTION CHAMBER FOR COMBUSTION RATE SHAPING AND EMISSIONS CONTROL IN PREMIXED-CHARGE COMBUSTION ENGINES. The co-pending application describes a combustion chamber design that can be effected to reduce flame speed, i.e, flame front propagation rate, for a portion of the combustion event, thus allowing some design control of peak cylinder temperatures or pressures to reduce knock occurrence and emissions while maintaining high engine efficiency.
However, it has heretofore not been possible to actively control heat losses from the flame produced by the combustion event. The present invention is directed to resolution of that problem as well as the problems associated with other prior control systems. It is desirable to have a system for actively controlling local flame speed within the combustion chamber of an internal combustion engine, and thereby control heat losses from the flame to the walls of the combustion chamber. Control of local flame speed and attendant heat losses to the cylinder walls permit reduction in NOx emissions, improved NOx control and higher engine efficiency without compromising emissions control. It is also desirable to have a means for controlling the temperature of the combustion chamber wall near the flame to modulate local heat transfer rate within the combustion chamber. Modulation of the local flame speed allows control of heat losses and permits combustion control for beneficial reductions in NOx emissions, improved NOx control and improved engine efficiency at given NOx emissions levels.
In accordance with one aspect of the present invention, an apparatus for the active control of the combustion rate of an air and fuel mixture in a combustion chamber of an internal combustion engine includes a movable member that is extendable through a predefined wall of the combustion chamber whereby the wall area of the combustion chamber is controllably modified during operation of the engine. The apparatus further includes a means for moving the movable member into and from the combustion chamber and a control means for controlling the movement of the movable member into and from the combustion chamber.
In accordance with another aspect of the present invention, an apparatus for the active control of the combustion rate of an air and fuel mixture in a combustion chamber of an internal combustion engine includes a stationary flame speed control member having an external surface extending into the combustion chamber and defining at least a portion of the wall of the combustion chamber adjacent to a portion of the combustion chamber where control of the flame speed of a combustion event in the combustion chamber is desired. The apparatus further includes a means for modulating the temperature of the external surface of the flame speed control member and a control means for controlling the means for modulating the temperature of the external surface of the flame speed control member.
In accordance with yet another aspect of the present invention, a method for actively controlling the combustion rate of an air and fuel mixture in a combustion chamber of an internal combustion engine includes sensing at least one engine operating parameter of the engine and controllably extending a movable member into and retracting the member from the combustion chamber in response to a sensed value of the engine operating parameter.
In accordance with an additional aspect of the present invention, a method for actively controlling the combustion rate of an air and fuel mixture in a combustion chamber of an internal combustion engine having a flame control member with an external surface extending inwardly into the combustion chamber includes sensing at least one engine operating parameter of the engine and controllably modulating the temperature of the external surface of the flame control member that extends inwardly into the combustion chamber.